Some of your questions were a bit incomplete, but here's what we know.
During TM previews, (and TM's have confirmed that this is the game plan for regular guests in the coming months), we will queue outside Olivanders (they'll be erecting rope lines soon), a TM will count us off in groups of roughly 25 people. The Shopkeeper will ask who is there to buy their wands, and one of the group will be chosen, (maybe up to three on slower days with faster shopkeepers). The rest of us will get to see the show. The "chosen one" can chose to buy the wand he/she is given or pick a different one in Owl Post. We'll exit the shop through Owl Post where the rest of us can chose the wand we want.
As far as prices, to my understanding, the Olivander wands (of which there are a dozen or so styles, and apparently based off birthdates, etc) are all $25, so no worry that the wand that chooses your kid will cost a fortune. This $100 wand business was based off the price of the wand TV remote control. The replica wands are most likely Noble Collection wands which will be in the $30-50 range for single wands with sets costing more.
The only thing I still wonder is how we'll know what our wand choices are of these new, exclusively Olivanders, wands. Someone, I think a TM on Orlando United, suggested that the shopkeepers in Owl Post will be able to help us figure out which wand would have chosen us if we had been picked (minus the special effects).